A sealing device has been well known which is interposed between a stationary side member and a rotary side member like a bearing unit in the wheel suspension device of automobile in order to prevent water and dust from entering.
Several measures have been recently taken so as to realize fuel efficient vehicles and the reduction of rotary torque is sought for the bearing unit.
In order to reduce the friction force with the sealing member, the slidably contacting surface of the sealing member fixed to the core member with the slinger (referred to slidably contacting surface hereinafter) is executed with surface treatment or other member is interposed between the slidably contacting surface.
The following patent citations 1 (Japanese Patent Publication, H11-190351-A) and 2 (Japanese Patent Publication, 2003-282231-A) disclose that the slidably contacting surface is treated with some surface treatment.
The patent citation 1 describes a sealing member wherein a nitride layer or a nitrosulphurizing layer is formed on the slidably contacting surface in a condition that surface oxide is removed, and accordingly the outer surface can be reformed to have fine, flat and hard surface nature while thermal strain of a base material is restrained during formation of the layer. It describes that, as the result, the frictional coefficient of the sliding part of the sealing member becomes low and heat generation can be restrained even though oil film is consumed.
The patent citation 2 describes a seal for roller bearing wherein the slidably contacting surface is executed with hardening treatment or applied with a hard film having corrosion resistance and a rust-prevention property. It describes that, as the result, anti-abrasive wearing ability and anti-corrosion wearing ability are improved on the slidably contacting surface under the circumstances of dirty salt water, thereby reducing the wearing amount on the metal surface and improving the sealing ability and the sealing durability.
The patent citation 3 (Japanese Patent Publication, H09-79274-A) is an embodiment in which other member is interposed between the sealing member and the slidably contacting surface.
The patent citation 3 describes an oil seal device in which a heat shrinking tube is fitted to the peripheral surface of a rotary side member and a sealing member comes into sliding contact by a fixed margin with a smooth surface of the tube. It describes that, as the result, wearing of the sealing member can be remarkably reduced by utilizing the lubricity of the heat shrinking tube.